Secondary air systems are common in many vehicles and are used to add oxygen to exhaust gases, aiding in final burn off of undesirable emissions. Generally, secondary air systems operate by pumping fresh air into the exhaust with one-way check valves to direct airflow from an electromechanical air pump. The secondary air is injected into the exhaust manifold to help burn the rich air-to-fuel mixture needed at start up. The secondary air system is generally used during normal operation in vehicles with larger engines due to higher air-to-fuel loads.
Since secondary air systems generally comprise a number of junctions and hoses, as well as employ vacuum, hydraulics, and electronics to operate check valves, the identity and location of a failed component can be difficult to determine. Moreover, it is difficult to find out which, if any, components are incorrectly installed during assembly.